The semiconductor industry has progressed into nanometer technology process nodes in pursuit of higher device density, higher performance, and lower cost. In the course of integrated circuit (IC) evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component or line that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Despite advances in materials and fabrication, scaling either planar (e.g., the planar FET) or three-dimensional (e.g., the FinFET) devices has proven challenging. For example, such scaling-down reduces the size of the area that can be used to connect a transistor to other components. Accordingly, an interconnect structure with such a limited area may disadvantageously impact a respective junction resistance, which in turn may degrade the transistor's switching speed.
A variety of technologies have been proposed to overcome this. Among them, a silicide layer formed between a transistor's source/drain feature and a respective interconnect structure (e.g., a source/drain contact) is typically used to decrease the junction resistance. Generally, a pre-clean process (e.g., one or more etching processes) is performed before forming the above-mentioned silicide layer. Although the pre-clean process advantageously removes undesirable residues/particles (e.g., oxides), the pre-clean process may also cause some damage to peripheral components and structures given the pre-clean process's isotropic characteristic. The damage to the peripheral components and structures (e.g., a spacer layer, an inter-layer dielectric layer, etc.) may in turn cause a bridge to be formed between a gate electrode and a source/drain contact, which may induce a variety of issues such as, for example, a short circuit. Thus, the existing technologies to form a source/drain contact of a transistor have not been entirely satisfactory.